1. Field of the Invention
This invention relates to the operation of a cooling tower used to cool water which is circulated for indirect heat exchange with warmer fluids. The invention further relates to methods of preventing scale buildup in the cooling tower and circulation system by maintaining preset levels of pH and electrical conductivity of the water. It also relates to time-delay systems for preventing large fluctuations in pH and conductivity as those variables are being maintained at the preset levels.
2. Description of the Prior Art
In a system in which water is used for indirect heat exchange with the fluids being processed, the warmed water is passed through a cooling tower wherein it is cooled and collected for recirculation. The water entering the tower is cooled by air from the outside as the water drops from the place of entry in the top of the tower to the basin in the bottom of the tower. During the process, some of the water evaporates and some is carried from the tower entrained by the air. A result of this water loss is an increase in the concentration of dissolved solids, or salts, in the cooling system water. To prevent an excessive increase in salts concentration, water from the system is discharged in an operation known as "blowdown," and the evaporated water, water lost by entrainment, and water lost to blowdown are replaced with fresh, or makeup, water.
To prevent precipitation of the ions in solution, thus forming scale on the surfaces of the system and reducing the efficiency of heat exchange, the pH of the water must be lowered by the addition of an acid. In systems for controlling pH and salts concentration, a problem which arises is wide fluctuations in pH or conductivity, a measurement related to salts concentration, caused by rapid or excessive addition of acid or excessive blowdown. Too large an addition of acid increases the corrosiveness of the water and excessive blowdown results in the waste of acid and other additives present in the discharged water. It would thus be desirable to regulate the addition of acid to the cooling system water so as to avoid large fluctuations in pH, which result in temporary high concentrations of corrosive acids in the system and difficulty in obtaining accurate continuous pH measurements. It would also be desirable in conjunction with such a process to have a method of regulating blowdown of the system so as to prevent waste of water and water additives from excessive blowdown.
It is thus an object of the invention to monitor and control the acidity and salts concentration and thus to minimize scale formation in a circulating water system. It is a further object to add acid to cooling system water and replace water having a high salts concentration with fresh water in such a way as to minimize fluctuations in pH and electrical conductivity, thus making more accurate control of salts buildup possible, minimizing the corrosiveness of the water solution, and reducing waste of water and water additives.